This is a research study designed to examine the effects of treating a disease known as secondary hyperparathyroidism (HPT) with an experimental drug known as AMG 073. The Goal of this research study is to look at the effect of AMG 073 on subjects with secondary HPT who are on hemodialysis. It is hoped that this study will provide early information on how well AMG 073 controls the parathyroid hormone (PTH) levels, and provide additional safety information. AMG 073 may offer a new approach to the treatment of secondary HPT by decreasing the production of PTH by the parathyroid glands. This study has been done in two phases, a single dose (one dose of medication) and a multiple dose (daily medication over a period of 8 days) phase. Enrollment in the multiple dose phase is complete. Fifty-two patients are expected to enter into the single dose phase, which will test six separate dose levels. Forty patients will receive the experimental drug AMG 073 and ten will receive placebo (a sugar pill or dummy medication).